The practice of producing vehicle components from two or more deep-drawn metal sheets that are connected by beading and adhesive bonding in the beading seam is known from the motor vehicle industry. While the adhesive is curing, the sheets may move relative to one another and, as a result, shape retention by the component is not assured. This is why two components that have already been connected by means of a positive-locking joint, preferably a seamed or beaded joint, are fixed relative to one another for the curing process. This is generally accomplished by means of resistance pressure welding.
External vehicle components, such as doors and hoods, are generally composed of a plurality of sheets which are connected in certain sections in the edge region by means of a seamed joint. The seamed joint is intended to avoid sharp edges in the edge region and the seamed joint, in combination with joining and sealing adhesive, ensures a rigid structure of the assembly.
To join such an assembly together, the usual practice is to apply a bead of adhesive to the edge region of a first part with a beading flange, which will subsequently form the outer skin. This can take place in the seaming bed or in an earlier work step. A second part, which forms an inner reinforcing structure, is then placed on or in the first part. The two parts are then partially or fully connected in a positive-locking manner in the edge region by seaming or beading. This may be accomplished by a process in which the beading flange is beaded around the edge of the inner part. During seaming, the adhesive is distributed fully over the contact surfaces of the parts and fills the flange cavities. This is intended to ensure a higher strength joint and corrosion protection.
The parts connected to one another or formed by beading are then generally welded to one another in the region of the beaded flange by means of welding tongs. Apart from providing a flow of current for the actual welding process, the welding tongs also apply a certain force required for good welding results and ensure that the parts are fixed relative to one another.
Since the assemblies mentioned are visible components which play an important role in determining the impression of quality made by the vehicle, the requirements on the geometrical tolerances and surface finish of the visible surface are extremely high.
However, a visible impression (e.g. welding mark) may be produced on both sides of the flange with conventional welding methods, and this is unwanted, especially on the outer or exterior-facing side of the component.
It is known to employ a tong-type welding apparatus, by means of which welding can be performed directly on a beaded edge or flange of a clamped component, for which purpose the joining electrode is placed directly on the flange or edge, usually on what is to be the interior-facing or inner side or the component. On the opposite side of the flange from the joining electrode, an abutment of the tong-type welding apparatus is urged against the flange. The counter-electrode is likewise placed on the inner side of the component, although not directly on but rather only in the vicinity of the flange.
Despite these modifications, however, there may still be unwanted impressions (e.g. distortions) on the resulting exterior-facing side of the component since the abutment of the tong-type welding apparatus clamps the component locally during welding and thus exerts a locally restricted pressure on the component and possibly also moves relative to the support. Combined with the high temperatures during welding, this frequently gives rise to distortions or deformations in the surface of the component on the abutment side.